Some manufacturing plants use loose abrasive materials for cleaning and grinding the surfaces of semi-finished products such as metal castings. Floor conveyors, worm conveyors, vibration conveyors, bucket elevators and integrated cleaning equipment, connected to containers, are used for the collection and sorting of such loose materials. The most common type of floor conveyor used is a rake conveyor with a horizontal plane surface which rakes with reciprocal movement above the horizontal surface; the rakes are attached to a supporting frame, which reciprocates in the horizontal direction. The driving units of known rake conveyors are located on the plane of the equipment. The workplace floor is located above the rake conveyors, and the floor consists of a supporting grate with mesh size of around 35×35 mm.
The disadvantage of these rake conveyors is that the abrasive material is either not actively removed from the places where the driving units are located, or the drives are located in rooms adjacent to the workplace, which increases space requirements. Other disadvantages of the existing systems are the difficult installation of rake conveyors using several drives and the fact that with the equipment described above, some small parts that are long and thin may fall through the supporting grate. This leads to parts accumulating on the floor of the workplace, e.g. screws or pieces of wire which may get stuck and cause the rake conveyor to fail.
Other existing systems contain two perpendicular conveyors that work on two planes (called a “lengthwise conveyor” and a “cross conveyor”), or in rare cases on one plane. A lengthwise conveyor is usually located above the cross conveyor, and the cross conveyor transports the loose material into a bucket conveyor outside the workplace. The disadvantages of these systems are the decreased load capacity of the floor at places where the conveyors cross and the unequal footing depth and increased costs for the construction of the foundation.
Worm conveyors are also utilized for horizontal transportation. The disadvantage of these conveyors is the difficult extension of worms to lengths exceeding 6 m, as the worms tend to sag at longer lengths. Another disadvantage of worm conveyors is doubled energy consumption in comparison to rack conveyors and the more expensive structural preparation of the floor.
Vertical bucket conveyors are typically connected to horizontal conveyors. The disadvantage of the connection to rack conveyors with a horizontal underlay surface is that when the bucket conveyor is connected to a rack conveyor at the same level, some spaces can occur from which the abrasives cannot be taken up by the bucket conveyor. On the other hand, a design in which the bucket conveyor is connected at a level lower than the rack conveyor requires other structural adaptations.
Vibration conveyors are also utilized for horizontal transportation. Their disadvantage that the building has to be tall to accommodate such a conveyor, which is unfavourable especially at long distances.
The bucket conveyors used in the past in air blasting are exclusively a single-row type. The use of a single-row type of bucket conveyor requires a large transportation height because of the column arrangement of the following equipment such as cleaners, silos, blasting equipment, etc. In such cases, the total height of the conveyors is about 3 m higher than in the system of the invention, and their structure sometimes reaches into the higher floors of the building or even above the roof structure. Another disadvantage is the necessity of installing the lower part of the bucket conveyor under the floor level. Because the belt is long, it stretches, which requires more frequent checking and tightening of the belt.
Double-row bucket conveyors are known from the design of sweeping machines, where it is used for connecting the input and output worm conveyors with the integrated cleaning apparatus for abrasives. The disadvantage of this design is that it cannot be used in workplaces where the large-area collection of abrasives is required in connection with blasting by pressurised air.